The above is a basic HTML game that fulfills the requirements mentioned. It is a simple 2D pixelated war game between alien races. The player controls a spaceship using the right and left arrow keys. They can shoot bullets using the spacebar to destroy enemy alien spaceships. If the player collides with an enemy alien spaceship, the game ends and the score is displayed.
To run the game, save the above code into a .html file and open it with a web browser that supports HTML5 canvas and JavaScript execution.